One of the major assets
of an onken enclosure is the way the vents acted as a an incredibly well braced,
almost constrained layer, cabinet wall -- this was the 1st thing i realized on seeing
my 1st onken in an Audax project pamplet in the late 70s (the design actually goes
back to the Jensen UltraFlex). Exposure to Bill Perkin's PR-1 research & Bud
Fried's Model R & Q (and the classic Dynaco A25) showed the benefits of aperiodic enclosures.
One of these benefits is the way an aperiodic box can help to deal with T/S parameters
being curves not scalars -- as drive changes T/S parameters change meaning a typical
BR box is only optimally tuned for 1 volume level.

My favourite page in
Olson's Acoustics is the one with the graphs that show the affect of box shape on
diffraction and from this that a box with heavily champhered edges gets you most
of the way with little effort.

Inspired by a deep
regard for the look of Tony Gee's Solo 103, the miniOnken for the FR125s literally
came in a flash (one might consider the Solo 103 as the fonken for the FE103).
It turned out really well

Since we are also playing with small tube amplifiers (2-10W) we wondered whether
the much more efficient Fostex FE127e would fit in a miniOnken-like enclosure. Turns
out that except for some changes in the size of the port spacers it works really
well.

The Fonken & miniOnken are near aperiodic enclosures that provides balanced response
from about 60 Hz up to over 15k Hz with no crossovers. The long ports with a very
high aspect ratio naturally provide a port with high resistance. They can be made
fully aperiodic with the addition of foam plugs in the ports. This may be useful
to easier mate with a woofer -- or in the case of the miniOnken lean out the bass
in a room where it is otherwise overfull. The near-aperiodic nature is seen in the
Fonken impedance curves below -- it is indicated by the small peak on the lower side
of the resoance saddle.

The box structure is
quite inert to box-wall resonance induced colourations. Instead of brute-force, the
frequency of panel resonances is pushed up to where they are unlikely to ever be
excited -- effectively eliminating them. This is accomplished by the use of small
panels (no box wall has a greater unbraced panel span than 5" (250mm)), the
use of relatively thin, light, and stiff baltic birch plywood, and the driver braced
against a large portion of the mass of the box panel to spread that energy as thin
as possible.

The sonic character
of these two speakers are different. Each plays to a somewhat different strengths.
Which one fits your needs best might well be determined by what kind of amplidier
you have -- amplifier & speaker should always be consider as a system. Consider
the following.

The Fonken likes small
amps with highish output impedance like SETs, no-feedback push-pull. a whole new
wave of single-ended SS, and the new small digital amplifiers. Becuase they are ~6
dB more efficient you can get away with not much power -- 2-20 watts is fine.

The miniOnken likes larger
class A & Class AB PP amps with low output impedance -- typical receivers &
solid state amplifiers as well as push-pull tubes amp with feedback. Because of its
very flat frequency response it makes a good small control monitor for music or video
editing. Suggest 15-50 watts.

These speakers do really well with any sort of vocals, jazz, and simpler classical
music. Limits with more taxing music are how loud and how low a single 4” cone can
play. They work well in a home theatre with subwoofer support

For greater levels
& wide soundfield you could start with a set of BiFonkens or Bipoler miniOnkens
or these can be used to provide excellent extended midrange with the addition of
a woofer & super-tweeter.

The advent of home
theatre has made the sub-woofer an accepted piece of kit and even a modest tweeter
can give more than acceptable performance if crossed over in the 12-20k range you'd
need - and the crossover can be a single capacitor.

The bipolar versions are only one of a number of other enclosures that have evolved
from the original speaker/bass tuning concept. These serve different sets of user
needs. A Fonken floor-stander and for a simpiler to build rectangular box with classic
golden ratio proportions have been developed & built. Even more far-out versions
have been proposed1.

Plans linked are freely
available for non-commercial use only.

Finished versions of
the miniOnken with planet10-hifi modified drivers (also available separately) can
be special ordered and flat-paks are under development.